Crown calix[4]arenes, method of preparation and use for selective extraction of caesium

ABSTRACT

The invention relates to new calixarenes of formula: ##STR1## in which R 1  represents a crown ether chain that includes at least two aryl or cycloalkyl rings, 
     R 2  is a hydroxyl or alkoxy group, or the two R 2  groups together form a crown ether chain such as R 1 , and R 3  represents a hydrogen atom or an alkyl group. The calixarenes are used to selectively extract caesium from aqueous solutions that notably have high concentrations of sodium.

TECHNOLOGICAL FIELD

The subject of this invention is crown calix[4]arenes, their method of preparation and their use for the selective extraction of caesium.

To put it more precisely, the invention relates to crown calix[4]arenes capable of selectively extracting caesium present in trace amounts in acid solutions, that may or may not have high concentrations of cations, such as the aqueous effluents arising from spent nuclear fuel reprocessing plants.

In these effluents, caesium 137 is one of the most noxious fission products due to its long half-life (30 years). It is therefore of interest to selectively remove it from liquid effluents coming from reprocessing plants, in particular from evaporator concentrates and acid solutions that may or may not have high salinity due, in particular to the presence of sodium nitrate.

Given the great similarity of the chemical properties of sodium and caesium, it is extremely difficult to selectively extract the caesium present in these effluents, at a concentration generally lower than 10⁻⁶ mol/l, while the concentration of sodium is about 4 mol/l.

In acid solutions of fission products, it is equally important to remove the ¹³⁵ Cs with a half life of 2×10⁶ years, with the intention either of transmuting it or incorporating it into a specified matrix, caesium being one of the most mobile elements in geological storage.

STATE OF THE PRIOR ART

In order to resolve this problem, it has been proposed to extract caesium using macrocyclic ligands such as the para tert-butyl-calixarenes described in U.S. Pat. No. 4,477,377. The para tert-butyl-calixarenes used are the tetramer, the hexamer and the octamer and the best results are obtained with the hexamer and the octamer, the tetramer not having very good selectivity for the separation of caesium from potassium. This technique for extracting caesium is interesting but its main disadvantage is that it is only applicable to aqueous basic solutions while most effluents arising from reprocessing are acid solutions.

More recently, for this separation the use of other calixarenes has been considered, in particular crown calixarenes as described in documents WO-A-94/12502 and WO-A-94/24138.

According to these documents, the one or two calixarene crowns are mainly made up of --C₂ H₄ --O-- chains which comprise from 4 to 7 atoms of oxygen.

The results obtained with crowns with 6 or 7 atoms of oxygen are satisfactory for the extraction of caesium from acid solutions which are not highly loaded with salts. On the other hand, when they are used with effluents highly loaded with sodium, containing, for example 4 mol.l⁻¹ of NaNO₃, their performance is clearly reduced. Also research has been pursued to find other extraction agents of the same type having improved performance in highly saline acid media.

The precise objective of this invention is new crown calixarenes which allow the selective extraction of caesium from acid solutions and the separation of it from sodium with better efficiency.

DESCRIPTION OF THE INVENTION

According to the invention, the calixarenes are crown calix[4]arenes of formula: ##STR2## in which: R¹ represents a group of formula:

    O--(CH.sub.2 CH.sub.2 O).sub.m --(XO).sub.n --(CH.sub.2 CH.sub.2 O).sub.p --(YO).sub.r --(CH.sub.2 CH.sub.2 O).sub.s                (II),

where X and Y, which can be identical or different, represent an arylene or cycloalkylene group, m, n, p, r and s are whole numbers such that:

    m=s=1,

    1≦n≦3,

    p=0 or 1

    r=0 or 1,

R² represents an OH group or an alkoxy group with from 1 to 18 carbon atoms, the two R² groups can be identical or different, or the two R² groups together form a group of formula:

    O--(CH.sub.2 CH.sub.2 O).sub.m --(XO).sub.n --(CH.sub.2 CH.sub.2 O).sub.p --(YO).sub.r --(CH.sub.2 CH.sub.2 C).sub.s                (II),

in which X, Y, m, n, p, r and s are as defined above; and

R³ represents a hydrogen atom or an alkyl group with 1 to 3 carbon atoms, with the condition that, in the case where the two R² groups together form a group of formula (III), p and r will not both be equal to 0 when n=1.

In the formula given above, the alkoxy groups used for R² can be straight chain or branched chain and are not necessarily identical.

Generally, they comprise from 1 to 18 atoms of carbon, preferably from 1 to 12 atoms of carbon.

In the formula given above, by "cycloalkylene group" one understands a bivalent group derived from a cyclic hydrocarbon by the removal of a hydrogen atom from each of two carbon atoms in the ring. As an example of such a group, one may mention the cyclohexylene group. The cycloalkylene groups used for X and Y generally comprise from 6 to 14 atoms of carbon.

In this formula, by "arylene group", one understands a group derived from an aromatic hydrocarbon comprising one or more aromatic rings or a heterocyclic ring including a heteroatom such as O, S or N, by the removal of an atom of hydrogen from each of two carbon atoms in the ring.

As examples of such groups one may mention phenylene, naphthylene, benzylene, pyridylene and thienylene groups.

In the calixarenes of the invention, the presence of one or two crown ether chains R¹ that include from 2 to 6 cyclic groups, for example phenylene groups, confers on the molecule greater rigidity of the crown and improves its extractive properties and its selectivity with respect to caesium in relation to sodium, in particular in a highly saline medium as will be seen below.

According to a first embodiment of the invention, the crown calix[4]arene of formula (I) includes a single crown ether chain. In this case, the two R² groups of formula (I) represent an hydroxy group and an alkoxy group.

According to a second embodiment of the invention, the crown calix[4]arene of formula (I) includes two crown ether chains which are preferably identical. In this case, the two R² groups together form a group identical to R¹.

According to the invention the crown ether chain or chains represented by R¹ and corresponding to formulae II, IIa or IIb can include from 2 to 6 saturated cyclic or aryl groups. Generally it is preferable to use aryl groups such as phenylene groups.

Good results for the selective extraction of caesium are obtained when the crown calix[4]arene includes one or two crowns R¹ of formula: ##STR3## Generally, in the calixarenes of the invention, R³ represents an atom of hydrogen.

The crown calixarenes of formula (I) of the invention can be prepared from corresponding calixarenes by reaction with a ditosylate that includes the R¹ group.

Hence, the crown calixarenes with a single crown, corresponding to the first embodiment of the invention can be prepared by reaction of a calix[4]arene of formula: ##STR4## in which R² and R³ are as stated above, with a ditosylate of formula (VI): ##STR5## in which R¹ is as stated above.

The crown calixarenes with two crowns corresponding to the second embodiment of the invention of formula (Ia): ##STR6## in which R¹ and R³ are as defined above, can be prepared by reaction of a calix[4]arene of formula: ##STR7## with a ditosylate of formula: ##STR8## in which R¹ is as stated above.

In order to carry out this reaction of forming the R¹ crown or crowns, the calixarene of formula (V) or (VII) is dissolved in a suitable solvent, for example, benzene or acetonitrile, a salt such as caesium carbonate and the ditosylate of formula (VI) are added, and the mixture is left to react under reflux for a period of time sufficient to form the R¹ crown or crowns by linking two benzene rings opposite one another. After reaction, the solvent is evaporated, the residue is taken up in hydrochloric acid and the product obtained is purified by the usual methods.

The calixarene of formula (V) used as starting product for the preparation of the single crown calix[4]arene can be prepared from the calix[4]arene of formula (VII) by reaction with a tosylate of formula: ##STR9## in which R² is as stated above.

The ditosylates of formula (VI) used as starting products for the preparation of the single crown and double crown calixarenes can be prepared by the usual methods from a diphenol such as catechol, or from a derivative of phenol in order to establish the O--CH₂ --CH₂ --O bonds or the ##STR10## linkages of the R¹ chain.

Hence, for the case where R¹ represents the group of formula: ##STR11## one can prepare the tosylate by carrying out the following steps: a) synthesis of the 2-(2-hydroxyethoxy)phenol of formula: ##STR12## by reaction of catechol with ethylene carbonate b) reaction of the 2-(2-hydroxyethoxy)phenol obtained in a) with ethylene glycol ditosylate to obtain 1,2-bis[2-(2-hydroxyethoxy)phenoxy]ethane, and

c) preparation of the tosylate by reaction of the 1,2-bis[2-(2-hydroxyethoxy)phenoxy]ethane with tosyl chloride of formula: ##STR13##

One can also prepare this tosylate by carrying out the following steps:

a) reaction of catechol with 2-chloroethanol to obtain 2-(2-hydroxyethoxy)phenol of formula: ##STR14## b) reaction of the 2-(2-hydroxyethoxy)phenol obtained in a) with 1,2-dibromoethane to obtain 1,2-bis[2-(2-hydroxyethoxy)phenoxy]ethane and

c) preparation of the tosylate by reaction of 1,2-bis[2-(2-hydroxyethoxy)phenoxy]ethane with tosyl chloride of formula (X): ##STR15##

In the case where R¹ represents the group with formula (IV), the tosylate can be prepared by carrying out the following steps:

a) preparation of the diphenol of formula: ##STR16## b) reaction of the diphenol with ethylene glycol ditosylate.

This tosylate can also be prepared by carrying out the following steps:

a) preparation of the diphenol of formula: ##STR17## b) reaction of the diphenol with tosyl chloride: ##STR18##

The crown calix[4]arenes of formula (I) previously described can be used, in particular for the selective extraction of caesium present in aqueous solutions, notably acid solutions loaded or not loaded with sodium such as dissolution solutions and aqueous effluents arising from spent nuclear fuel reprocessing plants.

For the extraction of caesium, the starting aqueous solutions can be acid solutions, for example nitric acid solutions containing from 10⁻³ to 7 mol/l nitric acid.

In order to carry out this extraction, the starting aqueous solution, called the first aqueous solution, containing the caesium is brought into contact with an immiscible liquid phase including the crown calix[4]arene, then the immiscible liquid phase is separated from the first aqueous solution.

The caesium can then be recovered in a second aqueous solution by bringing the immiscible liquid phase which has extracted the caesium into contact with a second aqueous re-extraction solution. The latter can be made up of distilled water and de-ionised water.

To implement this method, the first solution and the second solution can be contacted with the immiscible liquid phase using traditional extraction equipment such as mixer-decanters, pulsed columns etc.

This bringing into contact can also be carried out by arranging the immiscible liquid phase that includes the crown calix[4]arene as a liquid membrane comprising two opposite surfaces. The first starting aqueous solution containing the caesium is in contact with one of the surfaces of the membrane while the caesium extracted by the liquid membrane is recovered in the second aqueous re-extraction solution which is in contact with the other surface of the membrane.

To form the immiscible liquid phase, the crown calix[4]arene is dissolved in a suitable solvent.

By way of examples of solvents used, one can mention the alkyl benzenes and the nitrophenyl alkyl ethers.

Preferably, an ether such as ortho-nitrophenyl hexyl ether and ortho-nitrophenyl octyl ether is used as a solvent.

The concentration of the crown calix[4]arene in the immiscible liquid phase, depends, in particular on the solvent used. Concentrations ranging from 10⁻⁴ to 5×10⁻¹ mol/l can be used, for example a concentration of 10⁻² mol/l.

According to the invention, the immiscible phase can also be a solid phase. In the case of a solid phase, this can be impregnated with one or more calixarenes of the invention, in the pure state or in solution in a suitable solvent. One can also use a solid phase onto which the calixarene or calixarenes of the invention are grafted.

In the case where one is using a solid immiscible phase, this can be made up of a solid support onto which the calixarene is fixed. This can be in the form of a supported liquid membrane made up of a microporous membrane playing the role of support, the pores of which are filled with calixarene in solution in a suitable organic solvent.

This microporous membrane can be produced in polypropylene, in polyvinylidene fluoride or in polytetrafluoroethylene, and it can be used as a separation between a first compartment in which there is the first aqueous solution which is to be treated and a second compartment in which there is the second aqueous re-extraction solution.

In order to obtain good extraction with the supported liquid membranes, it is advantageous to use membranes having low thickness, high porosity and a small pore diameter. These membranes can be used in the form of modules such as ultra modules or microfiltration modules with flat membranes or with hollow fibres which allow high fluid flow rates to be processed.

Other characteristics and advantages of the invention will be better apparent on reading the following examples given, it is understood for the purposes of illustration and which are non-limitative and make reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (1A and 1B) illustrates two synthesis diagrams for calixarenes conforming to the invention. In this figure, route A corresponds to a single crown calixarene and route B to a double crown calixarene.

FIG. 2 (2A and 2B) illustrates the synthesis diagram for another single crown calixarene conforming to the invention.

FIG. 3 (3A and 3B) illustrates the synthesis diagram for another double crown calixarene conforming to the invention.

FIGS. 4 and 5 are graphs illustrating the change in the concentration of caesium in the starting solution as a function of time (in hours), during the extraction of caesium by a bis-crown calixarene (FIG. 4) and by a single crown calixarene (FIG. 5).

DETAILED DESCRIPTION OF EMBODIMENTS

The examples which follow illustrate the preparation of calix[4]arenes conforming to the invention and their use for the extraction of caesium from acid aqueous solutions loaded or not loaded with salts.

Examples 1 and 2 illustrate the preparation of single crown calixarenes, and examples 3 and 4 illustrate the preparation of bis-crown calixarenes.

EXAMPLE 1 Preparation of 25,27-dioctyloxy-calix[4]arene-dibenzo-crown-6 (compound 7)

This calixarene corresponds to formula (I) of the invention with R¹ representing the group with formula (III), the two R² groups representing the octoxy group and the R³ groups being an atom of hydrogen.

This synthesis is carried out in accordance with the reaction diagram illustrated in FIG. 1 (route A).

Steps a) and b) below use a synthesis method adapted from Yamaguchi, K., Negi, S., Kozaki, S., Nagano, R., Kuboniwa, H., Hirao, A., Nakahama, S., Yamazaki, N., Bull. Chem. Soc. Jpn.; 61, 2047-2054, 1988.

a) Synthesis of 2-(2-hydroxyethoxy)phenol (compound 2)

A mixture of catechol 1 (22 g, 0.2 mol), ethylene carbonate (17.6 g, 0.2 mol) and tetrabutyl ammonium iodide (2.4 g, 6.5 mol) is heated to 160° C. for about 1 hour until the release of CO₂ stops.

The mixture is purified by chromatography on a silica column using a (1:1) mixture of hexane and ethyl acetate as eluent and one obtains a white solid. 4.1 g of pure compound 2 is obtained by recrystallisation in water, which corresponds to a yield of 46%.

The characteristics of compound 2 are as follows:

Melting point: 100-101° C.

¹ H NMR (CDCl₃)δ(ppm): 6.95-6.80(m, 5H, ArOH and ArH), 4.13-4.10 (m, 2H, ArOCH₂), 4.0-3.97 (m, 3H, OCH₂ CH₂ OH). Mass spectrometry(IC): m/e=155 (M⁺).

b) Synthesis of 1,2-bis[2-(2-hydroxyethoxy)-phenoxy]-ethane (compound 3)

A mixture of compound 2 (2 g, 13 mmol) and NaH (0.32 g, 13 mmol) in 8 ml of dry dimethylformamide (DMF) is stirred for 30 minutes at ambient temperature. Ethylene glycol ditosylate (2.4 g, 6.4 mmol) dissolved in 25 ml of dry DMF is added drop by drop to this solution and the mixture is stirred at ambient temperature for 36 hours. After removing the DMF under vacuum, the residue is dissolved in dichloromethane and this is washed with water. The organic layer, dried over sodium sulphate is evaporated. 1.71 g of pure compound 3 is obtained by recrystallisation from a ethanol-water mixture (1:1), which corresponds to a yield of 81%.

The characteristics of this compound are as follows:

M. Pt.: 75-77° C.

¹ H NMR (CDCl₃)δ(ppm): 6.97-6.89(m, 8H, ArH), 4.39 (s, 4H, ArOCH₂ CH₂ OAr), 4.34 (s, 2H, OH), 4.1 (t, J=7 Hz, 4H, ArOCH₂ CH₂ OH), 3.87 (t, J=7 Hz, 4H, ArOCH₂ CH₂ OH).

Mass spectrometry(IC): m/e=335 (M⁺).

c) Synthesis of 1,2-bis[2-(2-hydroxyethoxy)-phenoxy]-ethane, bis(p-toluenesulphonate) (compound 4)

For this synthesis, a method adapted from Weber, E., J. Org. Chem.; 47, 1982, pages 3478-3486 is used.

A mixture of compound 3 (2 g, 5.9 mmol) and triethylamine (1.7 ml, 12 mmol) in 32 ml of dichloromethane is cooled to 0° C. Tosyl chloride (2.3 g, 12 mmol) and 4-dimethylaminopyridine (7.3 mg, 0.06 mmol) is added to this solution.

After 3 hours, the mixture is extracted with 50 ml of 10% HCl. The organic layer is dried over sodium sulphate and evaporated under vacuum. 2.3 g of pure compound 4 is obtained by recrystallisation from methanol, which corresponds to a yield of 60%. The characteristics of this compound are as follows:

M. Pt.: 91-93° C.

¹ H NMR (CDCl₃)δ(ppm): 7.75(d, J=8 Hz, 2H, ArOCH₃), 7.27 (d, J=8, 2H, ArCH₃), 6.86-6.81 (m, 8H, ArH), 4.34 (s, 4H, ArOCH₂ CH₂ OAr), 4.19-4.16 (m, 8H, TsOCH₂ CH₂ O), 2.39 (s, 6H, CH₃ Ar).

Mass spectrometry(IC): m/e=642 (M⁺)

d) Synthesis of compound 7

A solution of calix[4]arene 5 (1.0 g, 2.36 mmol) and potassium carbonate (0.48 g, 3.53 mmol) in 15 ml of dry acetonitrile is refluxed under an atmosphere of nitrogen for 30 minutes.

After adding octyl tosylate (2.01 g, 7.07 mmol), the mixture is refluxed for 48 hours. Then the acetonitrile is removed under reduced pressure and the residue treated with 50 ml of 10% HCl and 50 ml of dichloromethane. The organic layer is separated, washed twice with distilled water, dried over magnesium sulphate and then the dichloromethane is removed by distillation. Ethanol is then added and the precipitate is separated by filtration. 1.3 g of a white solid is obtained (yield of 85%) corresponding to 25,27-di-octoxy calix[4]arene 6.

It is dried under forced vacuum for several hours and dissolved in 310 ml of acetonitrile. An excess of caesium carbonate (2.64 g, 8.1 mmol) and the compound 4 (1.3 g, 2.02 mmol) is added under an atmosphere of nitrogen. The reaction mixture is refluxed for 16 hours and then treated with 10% HCl. Washing and separation are carried at as in the case of compound 6.

In this way 1.07 g of compound 7, 25,27-di-octoxycalix[4]arene-dibenzo-crown-6 is obtained, (a yield of 56%) from the oily residue by chromatography on a silica column using a mixture of tetrahydrofurane THF and hexane (1:9) as eluent and by crystallisation from methanol.

The characteristics of compound 7 are as follows:

M. Pt=130° C.

¹ H NMR (CDCl₃)δ(ppm): 7.10-6.99 (m, 12H, ArH), 6.80 (t, J=6.5 Hz, 2H, ArH para), 6.78 (d, J=6.5 Hz, 4H, ArH meta), 6.58 (t, J=6.5 Hz, 2H, ArH para), 4.37 (s, 4H, ArOCH₂ CH₂ OAr), 3.77 (s, 8H, ArCH₂ Ar), 3.63 (t, J=6 Hz, 4H, ArOCH₂ CH₂ OArO), 3.47 (t, J=6 Hz, 4H, ArOCH₂ CH₂ OArO), 3.36 (t, J=6 Hz, 4H, ArOCH₂ R), 1.36-1.1 (m, 24H, OCH₂ (CH₂)₆ CH₃), 0.92 (t, J=6.5 Hz, 6H, --CH₃)

Mass spectrometry (IC): m/e=948 (M⁺)

EXAMPLE 2 Synthesis of 1,3-dioctoxy calix[4]arene-tribenzo-crown-6 (compound 15).

This compound corresponds to formula (I) of the invention with R¹ representing the group with formula (IV), the two R² groups representing the octoxy group and R³ representing an atom of hydrogen.

This synthesis corresponds to the diagram illustrated in FIG. 2.

For this synthesis, the same method is followed as in Example 1, reacting as in step d) of Example 1, the ditosylate 14 corresponding to the group R¹ of formula (IV) with the compound 6, or 25,27-dioctoxy calix[4]arene.

The ditosylate is obtained as shown in the synthesis diagram illustrated in FIG. 2. This synthesis is carried out following the method described by D. E. Kime, J. K. Norymbersky, J. Chem. Soc. Perkin Trans. 1, 1977, page 1048, to prepare compound 13.

Compound 13 is then treated with an excess of ethylene glycol di-p-toluene sulphonate in dry DMF with sodium hydride for 8 hours. The DMF is removed under reduced pressure and compound 14 is purified by column chromatography.

Subsequently, this compound 14 is reacted with the calix[4]arene 6 from Example 1 following the same method of operation as in Example 1.

The characteristics of compound 15 obtained in this way are as follows:

¹ H NMR (CDCl₃)δ(ppm): 7.22-6.75 (m, 24H, ArH), 3.78 (s, 8H, ArCH₂ Ar), 3.65 (t, J=6 Hz, ArOCH₂ CH₂ OAr), 3.43 (t, J=6 Hz, ArOCH₂ CH₂ OAr), 3.36 (t, J=6 Hz, 4H, ArOCH₂ (CH₂)₆ CH₃), 1.3-1.1 (m, 24H, OCH₂ (CH₂)₆ CH₃), 0.90 (t, J=6.5 Hz, 6H OCH₂ (CH₂)₆ CH₃).

Mass spectrometry (IC): m/e=994.5 (M⁺).

EXAMPLE 3 Synthesis of calix[4]arene-bis-dibenzo-crown-6, compound 16.

This compound corresponds to formula (I) of the invention with R¹ representing the group with formula (III), the two R² groups forming together the group with formula (III) and R³ representing an atom of hydrogen.

For this synthesis, the reaction diagram shown in FIG. 1, route B, is followed. Hence one starts with catechol, compound 1, used as starting product in Example 1 and one converts it into compound 2, then into compound 3 and into compound 4 by working in a way that is only slightly different. Subsequently calix[4]-bis-crown is prepared by reaction of compound 4 with compound 5.

a) Preparation of compound 2

33.03 g (300 mmol) of catechol 1, 24.15 g (300 mmol) of 2-chloroethanol, 20.75 g (150 mmol) of K₂ CO₃ and 750 ml of acetonitrile are put into a 1 l flask. The reaction mixture is refluxed for 48 hours. It is then allowed to return to ambient temperature, the solution is filtered and is concentrated. After purification by column chromatography (CHCl₃ /acetone: 80/20), compound 2 is recovered in the form of a white solid (18.5 g); a yield of 40%.

NMR ¹ H spectrum in CDCl₃ at 200 MHz, δ in ppm

δ=6.99 to 6.78 (m, 4H, Ar)

δ=4.16 to 4.11 (m, 2H, OCH₂ CH₂)

δ=4.03 to 3.98 (m, 2H, OCH₂ CH₂ OH)

δ=2.79 (s, broad, 2H, OH).

b) Preparation of compound 3

7.71 g (50 mmol) of compound 2, 69.1 g (500 mmol) of K₂ CO₃, 5.64 g (30 mmol) of 1,2 dibromoethane and 750 ml of CH₃ CN are put into a 1000 ml flask. The reaction mixture is refluxed for 4 days. After having allowed it to return to ambient temperature, the solvent is evaporated to dryness. The residue thus obtained is dissolved in CH₂ Cl₂ and the K₂ CO₃ neutralised with 1N HCl. The organic phase is dried over sodium sulphate and then concentrated. After purification by column chromatography (CH₂ Cl₂ /acetone: 85/15), compound 3 is recovered in the form of a white solid (4.2 g).

Yield: 25%

NMR ¹ H spectrum in CDCl₃ at 200 MHz, δ in ppm

δ=6.97 (s, 8H, Ar)

δ=4.40 to 4.34 (m, 6H, OCH₂ CH₂ O and OH)

δ=4.14 to 4.10 (m, 4H, OCH₂ CH₂)

δ=3.89 to 3.86 (m, 4H OCH₂ CH₂).

c) Preparation of compound 4

2.0 g (6 mmol) of compound 3, 2.3 g (12 mmol) of tosyl chloride and 70 ml of dichloroethane are put into a 100 ml two necked flask. The reaction mixture is placed in an ice bath at 0° C. and then 2.3 g (22 mmol) of triethylamine is added drop by drop. After 48 hours of reaction at ambient temperature, the triethylamine is neutralised with a solution of 1N HCl. The organic phase is dried over sodium sulphate and then concentrated to give a beige solid. After purification by column chromatography (CH₂ Cl₂ /acetone: 95/5), the ditosylated product is recovered in the form of a white solid (2.4 g).

Yield: 62%

NMR ¹ H spectrum in CDCl₃ at 200 MHz, δ in ppm

δ=7.77 (d, 4H, J=8.5 Hz, system AB OTS)

δ=7.28 (d, 4H, J=8.5 Hz, system AB OTS)

δ=6.97 to 6.81 (m, 8H, Ar)

δ=4.31 to 4.27 (m, 8H, OCH₂ CH₂ O)

δ=4.20 to 4.16 (m, 4H, OCH₂ CH₂ O)

δ=2.40 (s, 6H, ArCH₃)

d) Preparation of compound 16

0.425 g (1 mmol) of calix[4]arene (compound 5) and 1.380 g (10 mmol) of K₂ CO₃ in 100 ml of CH₃ CN were put into a 250 ml flask. The mixture was stirred for 4 hours at ambient temperature, then 0.643 g (1 mmol) of ditosylate 4 is added and the mixture heated under reflux for 7 days. The same quantity of K₂ CO₃ and ditosylate is once again added to the solution and the reaction mixture is refluxed for 7 more days. After 14 days of reflux, the solvent is evaporated to dryness. The residue obtained is dissolved in dichloromethane and the K₂ CO₃ neutralised with 1N HCl. The organic phase is dried over sodium sulphate and then concentrated. After purification by column chromatography (CH₂ Cl₂ /acetone: 90/10), the compound 16 dibenzo-bis-crown-6 is recovered in the form of a white solid (850 mg).

Yield: 83%

NMR ¹ H spectrum in CDCl₃ at 200 MHz, δ in ppm

δ=7.14 to 7.08 (m, 8H, Ar)

δ=6.96 to 6.89 (m, 8H, Ar)

δ=6.72 (d, 8H, J=7 Hz, H meta to the Ar)

δ=6.58 (d, 8H, J=7 Hz, H para to the Ar)

δ=4.39 (s, 8H, OCH₂ CH₂ O)

δ=3.74 (s, 8H, ArCH₂ --Ar)

δ=3.49 (m, 16H, OCH₂ CH₂ O)

Mass spectrum FAB positive m/z=1021.5 (100%)

EXAMPLE 4 Synthesis of calix[4]arene-bis-crown-6 (compound 17).

This calixarene corresponds to formula (I) of the invention with R¹ representing the group with formula (IV), the two R² groups together forming the same group with formula (IV) and R³ representing an atom of hydrogen.

For this synthesis, the synthesis diagram given in FIG. 3 is followed. First the ditosylate is prepared from compound 8 used in Example 2, but by carrying out slightly different steps.

a) Preparation of compound 19

4.47 g (36 mmol) of Guaiacol 8 or 2-methoxyphenol, 24.88 g (180 mmol) of K₂ CO₃ and 350 ml of acetonitrile are put into a 500 ml flask. After having stirred the solution for 2 hours at ambient temperature, 4.25 g (18 mmol) of 1,2-dibromobenzene 18 is added drop by drop and the reaction mixture heated under reflux for 4 days. After having allowed the reaction mixture to return to ambient temperature, the solvent is evaporated to dryness. The residue thus obtained is dissolved in dichloromethane and the K₂ CO₃ neutralised with 1N HCl. The organic phase is dried over sodium sulphate, then concentrated. After purification by column chromatography (CH₂ Cl₂), the product is recovered in the form of a yellow solid (3.45 g).

Yield: 30%

NMR ¹ H spectrum in CDCl₃ at 200 MHz, δ in ppm

δ=6.95 to 6.85 (m, 12H, Ar)

δ=3.89 (s, 6H, CH₃).

b) Preparation of compound 13

10 g (40 mmol) of boron tribromide BBr₃ and 300 ml of dichloromethane is put into a 500 ml two necked flask. After having stirred the solution for 30 minutes at -60° C., 3.22 g (10 mmol) of 2,2-[1,2-phenylenedi(oxy) diphenyl dimethyl ether] 19 is added drop by drop while maintaining the temperature at -60° C. After 10 hours of reaction, the excess BBr₃ is destroyed by adding methanol. The residue obtained is evaporated to dryness, then dissolved in dichloromethane. The organic phase is washed with a 5% NaHCO₃ solution, then dried over Na₂ SO₄ and concentrated. A white solid is recovered by recrystallisation in n-heptane (2.6 g).

Yield: 88%

NMR ¹ H spectrum in CDCl₃ at 200 MHz, δ in ppm

δ=6.97 to 6.88 (m, 12H, Ar)

δ=6.58 (s, 2H, CH₃).

c) Preparation of compound 20

2.35 g (8 mmol) of 2,2'-[1,2-phenylenedi(oxy)diphenol] 13, 2.58 g (32 mmol) of 2-chloroethanol, 11 g (80 mmol) of K₂ CO₃ and 200 ml of acetonitrile are put into a 500 ml flask. The reaction mixture is refluxed for 3 days. After having allowed it to return to ambient temperature, it is evaporated to dryness. The residue obtained is dissolved in dichloromethane and the K₂ CO₃ neutralised with 1 N hydrochloric acid HCl. The organic phase is dried over sodium sulphate and then concentrated. After purification by column chromatography (CH₂ Cl₂ : acetone -90:10), the product 20 is recovered in the form of a white solid (1.9 g)

Yield: 62%

NMR ¹ H spectrum in CDCl₃ at 200 MHz, δ in ppm

δ=6.87 to 6.74 (m, 12H, Ar)

δ=4.32 (s, broad, 2H, OH)

δ=4.07 to 4.02 (m, 4H, OCH₂ CH₂)

δ=3.74 to 3.69 (m, 4H, OCH₂ CH₂)

d) Preparation of the ditosylate 14

1.8 g (4.7 mmol) of diethylene glycol triphenol 20, 1.8 g (9.4 mmol) of tosyl chloride and 60 ml of dichloroethane were put into a 100 ml two necked flask.

The reaction mixture is placed in an ice bath at 0° C. and then 2.3 g (22 mmol) of triethylamine is added drop by drop. After 48 hours reaction at ambient temperature, the triethylamine is neutralised with a 1N solution of hydrochloric acid HCl. The organic phase is dried over sodium sulphate and then concentrated to give a solid. After purification by column chromatography (CH₂ Cl₂ : acetone-98:2), the ditosylated product 14 is recovered in the form of a white solid (1.95 g).

Yield: 60%

NMR ¹ H spectrum in CDCl₃ at 200 MHz, δ in ppm

δ=7.84 (d, 4H, J=8.5 Hz, system AB OTS)

δ=7.37 (d, 4H, J=8.5 Hz, system AB OTS)

δ=6.89 to 6.78 (m, 12H, Ar)

δ=4.22 to 4.18 (m, 4H, OCH₂ CH₂)

δ=3.89 to 3.82 (m, 4H, OCH₂ CH₂)

δ=2.39 (s, 6H, ArCH₃)

e) Preparation of calixarene-bis-crown 17

0.425 g (1 mmol) of calix[4]arene 5, 1.380 g (10 mmol) of K₂ CO₃ in 100 ml of CH₃ CN is put into a 250 ml flask. The mixture is stirred for 4 hours at ambient temperature and then 0.691 g (1 mmol) of ditosylate 14 is added and the mixture heated under reflux for 7 days. The same quantity of K₂ CO₃ 1.38 g (10 mmol) and ditosylate 0.691 g (1 mmol) is once again added to the solution and the reaction mixture is refluxed for 7 more days. After 14 days of reflux, the solvent is evaporated to dryness. The residue obtained is dissolved in dichloromethane and the K₂ CO₃ neutralised with 1N HCl. The organic phase is dried over sodium sulphate and then concentrated. After purification by column chromatography (CH₂ Cl₂ /acetone: 90/10), the product tribenzo-bis-crown 17 is recovered in the form of a white solid (340 mg).

Yield : 30%

NMR ¹ H spectrum in CDCl₃ at 200 MHz, δ in ppm

δ=7.22 to 6.94 (m, 24H, Ar)

δ=6.69 (d, 8H, J=7 Hz, H meta to the Ar)

δ=6.55 (t, 4H, J=7 Hz, H para to the Ar)

δ=3.72 (s, 8H, Ar--CH₂ Ar)

δ=3.21 to 3.17 (m, 16H, OCH₂ CH₂ O)

The examples which follow illustrate how the calixarenes of the invention are used for the selective extraction of caesium.

EXAMPLE 5 Extraction of caesium

In this example, using calixarenes of the invention, caesium is extracted from an aqueous solution having a nitric acid concentration of 1 mol/l and containing 5×10⁻⁴ mol/l of CsNO₃.

For this purpose, a volume of aqueous solution is brought into contact with a volume of organic liquid constituted by ortho-nitrophenyl hexyl ether containing 10⁻² mol/l of calixarene. When equilibrium is reached, the caesium content of the organic liquid is measured by gamma spectrometry. Then the percentage caesium extracted is determined and the distribution coefficient DCS which corresponds to the ratio of the concentration of caesium in the organic liquid to the concentration of caesium in the aqueous solution at equilibrium.

For these experiments, the calixarenes from Examples 1 and 3 above were used. The results obtained are given in Table 1.

For comparison purposes, in Table 1, the results are also given that were obtained under the same conditions with calixarenes of the prior art, which are the calixarenes from Examples 3 and 6b in the document WO94/12502 and the calixarene bis-1,2-naphtho crown-6 and the single crown calixarenes of Examples 3, 4 and 6 in document WO94/24138.

EXAMPLE 6 Extraction of sodium

In this example, one starts with an aqueous solution having a nitric acid concentration of 1 mol/l, containing 5×10⁻⁴ mol/l of sodium nitrate. It is subjected to an extraction under the same conditions as those in Example 5, using a calixarene at a concentration of 10⁻² mol/l in ortho-nitrophenyl hexyl ether. As previously the sodium content of the organic solution is measured by gamma spectrometry and the percentage of sodium extracted and the distribution coefficient D_(na) are calculated.

The same calixarenes are used as in Example 5. The results obtained are given in Table 1.

EXAMPLE 7 Extraction of caesium

The same method of operation as in Example 5 is followed to extract the caesium from an aqueous solution of a composition different to that of Example 1, and which contains:

1 mol/l nitric acid

4 mol/l sodium nitrate, and

5×10⁻⁴ mol/l CsNO₃

The calixarenes and the solvent used are the same as those in Example 1.

The results obtained are given in Table 1.

The results in Table 1 show that the single crown and bis-crown calix[4]arenes of the invention extract caesium with good yields and separate it from the sodium also present in the effluents coming from reprocessing plants. Furthermore, they show that in the presence of high concentrations of sodium, the calixarenes of the invention permit selective extraction of much greater quantities of caesium while the opposite occurs with the calixarenes of the prior art.

In effect, Dc, increases from 31 to 56 or from 23 to 54 with the calixarenes of the invention while D_(Cs) decreases in all cases with the calixarenes of the prior art.

Therefore, with the calixarenes of the invention, a surprising effect on the extraction of caesium is obtained.

EXAMPLE 8 Transport of the caesium

In this example, the extraction of caesium-137 is carried out in the presence of sodium-22 starting with a solution containing 1 mol/l of nitric acid, 4 mol/l of NaNO₃, ¹³⁷ Cs and ²² Na with a caesium-137 activity of 1558 kBq/l and a sodium-22 activity of 505 kBq/l.

To carry out the extraction, a device is used that is separated into two compartments by a supported liquid membrane, constituted by a microporous membrane made of polypropylene sold under the name CELGARD 2500 and which has the following characteristics:

Porosity factor: 0.45

Diameter of the pores: 0.04 μm.

Thickness of the membrane: 0.025 mm.

The pores of this membrane are filled with an organic phase constituted by nitrophenyl hexyl ether that includes 0.01 mol/l of the calixarene from Example 3.

The two compartments of the device are each fitted with a magnetic stirrer. The first compartment contains 55 ml of the aqueous starting solution and the second compartment contains an aqueous re-extraction solution consisting of water. The effective surface area of the membrane is 11.6 cm².

During this test, the activity of the aqueous starting solution from the first compartment is determined by γ spectrometry and the percentage of caesium-137 extracted into the second compartment is deduced from this.

The results obtained are given in Table 2 and in FIG. 4.

This FIG. 4 represents the change in concentration of caesium in the re-extraction solution as a function of time (in hours).

The concentration of caesium is given in the y-co-ordinate by log (C/C₀) with C representing the concentration of caesium at time t and C₀ the initial concentration.

The transport corresponds to a permeability of the membrane to caesium-137 of 4.27 cm/h, that of sodium not being measurable; a permeability less than 0.1 cm/h.

EXAMPLE 9 Extraction of caesium-137

In this example, the same operating method is followed as in Example 8, using an aqueous starting solution containing 1 mol/l HNO₃, 4 mol/l of NaNO₃, ¹³⁷ Cs and ²² Na with a caesium-137 activity of 1549 kBq/l and a sodium-22 activity of 505 kBq/l. In this case, the pores of the membrane are filled with an organic phase made up of nitrophenyl hexyl ether including 0.01 mol/l of the single crown calixarene from Example 1. The re-extraction solution is water, as in Example 8.

The results obtained are given in Table 3 and in FIG. 5.

FIG. 5 shows the change in the concentration of caesium (in log C/C₀) in the re-extraction solution as a function of time (in hours).

Under these conditions, the permeability of the membrane with respect to caesium-137 is 4.19 cm/h, that of sodium less than 0.1 cm/h.

                                      TABLE 1                                      __________________________________________________________________________     Calixarene                      Example 6                                      Calixarene-bis-  Examples 4 and 5                                                                              CsNO.sub.3 5 × 10.sup.-4 M               crown-6          Cs(Na)NO.sub.3 5 × 10.sup.-4 M, HNO.sub.3                                               NaNO.sub.3 4M, HNO.sub.3 1M                    calixarene-bis-crown-6                                                                          D.sub.Cs                                                                           D.sub.Na                                                                             D.sub.Cs/Na                                                                         D.sub.Cs                                       __________________________________________________________________________     WO 94/12502 (Ex 3) Bis C6                                                                       19.5                                                                               1.3 × 10.sup.-2                                                                 1500                                                                               10                                             WO 94/12502 (EX 6b) Bis(1,2 Bz C6)                                                              32.5                                                                               1.7 × 10.sup.-3                                                                 19000                                                                              20                                             WO 94/12502 Bis(1,2 Np C6)                                                                      29.5                                                                               <10.sup.-3                                                                           >29500                                                                              8.1                                            Invention (Ex 3) Bis (Di 1,2 Bz C6)                                                             31  <10.sup.-3                                                                           >31000                                                                              56                                             Calixarene-monocrown-6                                                         WO 94/24138 (Ex 3) Di propoxy C6                                                                19.2                                                                               1.8 × 10.sup.-3                                                                 10500                                                                              12                                             WO 94/24138 (Ex 4) Di isopropoxy C6                                                             28.5                                                                               <10.sup.-3                                                                           >28500                                                                              18                                             WO 94/24138 (Ex 6) Di octyloxy C6                                                               33  <10.sup.-3                                                                           >33000                                                                              25                                             Invention (Ex 1) Dioctyloxy (Di 1,2 Bz                                                          23  <10.sup.-3                                                                           >23000                                                                              54                                             C6)                                                                            __________________________________________________________________________

                  TABLE 2                                                          ______________________________________                                                    .sup.137 Cs activity in the                                                    aqueous starting                                                    Time       solution     .sup.137 Cs extracted                                  (hours)    (kBq/l)      (in %)                                                 ______________________________________                                         0          1558          0.0%                                                  0.5        1192         23.5%                                                  1          1057         32.2%                                                  1.5        827          46.9%                                                  2          685          56.0%                                                  2.5        569          63.5%                                                  3          481          69.1%                                                  3.5        367          76.4%                                                  4          297          80.9%                                                  4.5        242          84.5%                                                  5          208          86.6%                                                  5.5        180          88.4%                                                  6          134          91.4%                                                  ______________________________________                                    

                  TABLE 3                                                          ______________________________________                                                    .sup.137 Cs activity in the                                                    aqueous starting                                                    Time       solution     .sup.137 Cs extracted                                  (hours)    (kBq/l)      (in %)                                                 ______________________________________                                         0          1549          0.0%                                                  0.5        1173         24.3%                                                  1          935          39.6%                                                  1.5        723          53.3%                                                  2          567          63.4%                                                  2.5        444          71.3%                                                  3.5        339          78.1%                                                  4.5        243          84.3%                                                  5          207          86.6%                                                  5.5        180          88.4%                                                  6          158          89.8%                                                  6.5        146          90.6%                                                  ______________________________________                                     

What is claimed is:
 1. A crown calix-4-arene corresponding to the formula: ##STR19## in which: R¹ represents a group of formula:

    O--(CH.sub.2 CH.sub.2 O).sub.m --(XO).sub.n --(CH.sub.2 CH.sub.2 O).sub.p --(YO).sub.r --(CH.sub.2 CH.sub.2 O).sub.s                (II),

where X and Y, which can be identical or different, represent an arylene or cycloalkylene group, m, n, p, r and s are whole numbers such that:

    m=s=1,

    1≦n≦3,

    p=0 or 1

    r=0 or 1,

R² represents an OH group or an alkoxy group with from 1 to 18 carbon atoms, the two R² groups can be identical or different, or the two R² groups together form a group of formula:

    O--(CH.sub.2 CH.sub.2 O).sub.m --(XO).sub.n --(CH.sub.2 CH.sub.2 O).sub.p --(YO).sub.r --(CH.sub.2 CH.sub.2 O).sub.s                (II),

in which) X, Y, m, n, p, r and s are as defined above; and R³ represents a hydrogen atom or an alkyl group with 1 to 3 carbon atoms, with the condition that, in the case where the two R² groups together form a group of formula (II) p and r will not both be equal to 0 when n=1.
 2. The crown calix-4-arene according to claim 1 corresponding to formula (I) with R² representing a OH group or an alkoxy group.
 3. The crown calix-4-arene according to claim 2 in which R¹ represents the group of formula: ##STR20## R² represents the octoxy group and R³ represents a hydrogen atom.
 4. The crown calix-4-arene according to claim 2 in which R¹ represents the group of formula: ##STR21## R² represents the octoxy group, and R³ represents an atom of hydrogen.
 5. The crown calix-4-arene according to claim 1 corresponding to formula (I) in which the two R² groups together form a group identical to R¹.
 6. The crown calix-4-arene according to claim 5 in which R¹ represents the group of formula: ##STR22## and R³ represents a hydrogen atom.
 7. The crown calix-4-arene according to claim 5 in which R¹ represents the group of formula: ##STR23## and R³ represents an atom of hydrogen.
 8. The crown calix-4-arene according to claim 1 in which R¹ represents the group of formula (III) or (IV): ##STR24##
 9. A method of preparation of a crown calix-4-arene corresponding to the formula: in which:R¹ represents a group of formula:

    O--(CH.sub.2 CH.sub.2 O).sub.m --(XO).sub.n --(CH.sub.2 CH.sub.2 O).sub.p --(YO).sub.r --(CH.sub.2 CH.sub.2 O),                     (II),

where X and Y, which can be identical or different, represent an arylene or cycloalkylene groups, m, n, p, r and s are whole numbers such that: =s=1, 1≦n≦3, p=0 or 1 r=0 or 1,R² represents an OH group or an alkoxy group with from 1 to 18 carbon atoms, and R³ represents a hydrogen atom or an alkyl group with 1 to 3 carbon atoms, comprised of reacting a calix-4-arene of formula: ##STR25## in which R² and R³ have the meanings stated above, with a ditosylate of formula (VI): ##STR26## in which R¹ has the meaning stated above.
 10. The method according to claim 9, in which R¹ being the group of formula: ##STR27## the tosylate be prepared by carrying out the following steps: a) synthesis of 2-(2-hydroxyethoxy)phenol of formula: ##STR28## by reaction of catechol with ethylene carbonate b) reaction of the 2-(2-hydroxyethoxy)phenol obtained in a) with ethylene glycol ditosylate to obtain 1,2-bis[2-(2-hydroxyethoxy)phenoxyl]ethane andc) preparation of the tosylate by reaction of 1,2-bis[2-(2-hydroxyethoxy)phenoxy]ethane with tosyl chloride of formula: ##STR29##
 11. The method according to claim 9 in which R¹ being the group of formula: the tosylate is prepared by carrying out the following steps:a) reaction of catechol with 2-chloroethanol to obtain 2-(2-hydroxyethoxy)phenol of formula: ##STR30## b) reaction of the 2-(2-hydroxyethoxy)phenol obtained in a) with 1,2-dibromethane to obtain 1,2-bis [2-(2-hydroxyethoxy)pbenoxy]etbane and c) preparation or the tosylate by reaction of 1,2-bis[2-(2-hydroxyethoxy)phenoxy]ethane with tosyl chloride of formula (X): ##STR31##
 12. The method according to claim 9 R¹ being the group of formula: the tosylate is prepared by carrying out the following steps:a) preparation of the diphenol of formula: ##STR32## b) reaction of the diphenol with ethylene glycol ditosylate.
 13. The method according to claim 9 in which R¹ represents the group of formula: ##STR33## the tosylate is prepared by carrying out the following steps: a) preparation of the diphenol of formula: ##STR34## b) reaction of the diphenol with tosyl chloride: ##STR35##
 14. A method of preparing a calix-4-arene corresponding to the formula: in which R¹ represents a group of formula:

    O--(CH.sub.2 CH.sub.2 O).sub.m --(XO).sub.n --(CH.sub.2 CH.sub.2 O).sub.p --(YO).sub.r --(CH.sub.2 CH.sub.2 O).sub.s                (II)

where X and Y, which can be identical or different, represent an arylene or cycloalkylene group, m, n, p, r and s are whole numbers such that: m=s=1, 1≦n≦3 p=0 or 1 r=0 or 1,R³ represents a hydrogen atom or an alkyl group with 1 to 3 carbon atoms, comprised of reacting calix-4-arene of formula: ##STR36## with a ditosylate of formula: ##STR37## in which R¹ has the meaning stated above.
 15. The method according to claim 14 in which R¹ being the group of formula: ##STR38## the tosylate is prepared by carrying out the following steps: a) synthesis of 2-(2-hydroxyethoxy)phenol of formula: ##STR39## by reaction of catechol with ethylene carbonate, b) reaction of the 2-(2-hydroxyethoxy)phenol obtained in a) with ethylene glycol ditosylate to obtain 1,2-bis[2-(2-hydroxyethoxy)phenoxy]ethane andc) preparation of the tosylate by reaction of 1,2bis[2-(2-hydroxyethoxy)phenoxy]ethane with tosyl chloride of formula: ##STR40##
 16. The method according to claim 14 in which R¹ being the group of formula: the tosylate is prepared by carrying out the following steps:a) reaction of catechol with 2-chloroethanol to obtain 2-(2-hydroxyethoxy)phenol of formula: ##STR41## b) reaction of the 2-(2-hydroxyethoxy)phenol obtained in a) with 1,2-dibromoethane to obtain 1,2-bis[2-(2-hydroxyethoxy)phenoxy]ethane and c) preparation of the tosylate by reaction of 1,2-bis[2-(2-hydroxyethoxy)phenoxy]ethane with tosyl chloride of formula (X): ##STR42##
 17. The method according to claim 14 R¹ being the group of formula: the tosylate is prepared by carrying out the following steps:a) preparation of the diphenol of formula: ##STR43## b) reaction of the diphenol with ethylene glycol ditosylate.
 18. A method according to claim 14 in which R¹ represents the group of formula: ##STR44## the tosylate is prepared by carrying out the following steps: a) preparation of the diphenol of formula: ##STR45## b) reaction of the diphenol with tosyl chloride: ##STR46##
 19. A method for the selective extraction of caesium from an aqueous solution that comprises of bringing this aqueous solution into contact with an immiscible liquid phase that includes a crown calix-4-arene corresponding to formula (I) ##STR47## R¹ represents a group of formula:

    O--(CH.sub.2 CH.sub.2 O).sub.m --(XO).sub.n --(CH.sub.2 CH.sub.2 O).sub.p --(YO).sub.r --(CH.sub.2 CH.sub.2 O).sub.b                (II),

where X and Y, which can be identical or different, represent an arylene or cycloalkylene group, m, n, p, r and s are whole numbers such that: m=s=1, ≦ n≦3, p=0 or 1 r=0 or 1,R² represents an OH group or an alkoxy group with from 1 to 18 carbon atoms, the two R² groups can be identical or different, or the two R² groups together form a group of formula:

    O--(CH.sub.2 CH.sub.2 O).sub.m --(XO).sub.n --(CH.sub.2 CH.sub.2 O).sub.p --(YO).sub.r --(CH.sub.2 CH.sub.2 O),                     (II),

in which X, Y, m, n, p, r and s are as defined above; and R³ represents a hydrogen atom or an alkyl group with 1 to 3 carbon atoms,with the condition that, in the case where the two R² groups together form a group of formula (II), p and r will not both be equal to 0 when n=1 separating the immiscible phase from the aqueous solution having extracted the caesium.
 20. The method according to claim 19, in which the immiscible liquid phase is a solution of the crown calix-4-arene in an organic solvent.
 21. The method according to claim 20, in which the organic solvent is a nitrophenyl alkyl ether.
 22. The method according to claim 21, in which the aqueous re-extraction solution is distilled an de-ionised water.
 23. The method according to claim 21, in which the immiscible liquid phase forms a liquid membrane, the aqueous solution containing the caesium is brought into contact with one surface of this membrane and the aqueous re-extraction solution is brought into contact with the opposite surface of this liquid membrane.
 24. The method according to claim 20 in which afterwards, the caesium is recovered into an aqueous re-extraction solution by bringing the liquid phase which has extracted the caesium into contact with an aqueous solution.
 25. The method according to claim 19, in which the aqueous starting solution is an aqueous effluent containing caesium with or without sodium arising from a spent nuclear fuel reprocessing plant.
 26. The method according to claim 19, in which the calix-4-arene corresponds to formula (I) in which R¹ represents the group of formula: ##STR48## the two R² groups together form the group with formula (III) and R³ represents a hydrogen atom.
 27. The method according to claim 19, in which the calix-4-arene corresponds to formula (I) in which R¹ represents the group of formula: ##STR49## the two R² groups represent the octoxy group and R³ represents a hydrogen atom. 